As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Similarly, for persons who have had their natural lens removed and an intraocular lens inserted as a replacement, the ability to accommodate is totally absent.
Among the methods used to correct presbyopia is the mono-vision system in which a person is fitted with one contact lens for distance vision and one lens for near vision. The mono-vision system permits the wearer to distinguish both distance and near objects, but is disadvantageous in that a substantial loss in depth perception results.
Another method for presbyopia correction is the use of contact lenses that provide distance and near vision power or distance, near and intermediate power. These lenses overcome the depth perception loss and typically use alternating concentric rings or alternating radial segments of distance and near power. However, these lenses are problematic in that they expose the wearer's retina to two images, one in and one out of focus. The two images are not disadvantageous for near vision because the out of focus distance objects being viewed in the near segments of the lens do not interfere, but contribute to the near vision resolution. The reason for this is that the out of focus distance objects are in an orientation that does not interfere with the near images.
However, such lenses are problematic for distance vision. As the wearer views distant objects through the lens, the near images go through focus before the distant images. As a result, the out of focus near images are inverted and interfere with the image of the distant object. Thus, a need exists for multifocal lenses that overcome the disadvantages of known lenses.